1. Field of the Invention
The present invention relates to a charged particle lithography apparatus, and in particular to an aperture array for a lithography system with a cooling system.
2. Description of the Related Art
Currently, most commercial lithography systems use a light beam and mask as a means to reproduce pattern data for exposing a target, such as a wafer with a coating of resist. In a maskless lithography system, beams of charged particles are used to write the pattern data onto the target. The beamlets are individually controlled, for example by individually switching them on and off, to generate the required pattern. For high resolution lithography systems designed to operate at a commercially acceptable throughput, the size, complexity, and cost of such systems becomes an obstacle.
Furthermore, existing charged particle beam technology is suitable for lithography systems for relatively course patterning of images, for example to achieve critical dimensions of 90 nm and higher. However, a growing need exists for improved performance. It is desired to achieve considerably smaller critical dimensions, for example 22 nm, while maintaining sufficient wafer throughput, e.g. between 10 and 100 wafers per hour. In order to achieve such a large throughput at ever decreasing feature sizes it is necessary to increase the number of beams generated by the system, increase the current in the charged particle beams, and reduce the distance between the beams.
Charged particle beam lithography systems are typically operated in a vacuum environment provided by a vacuum chamber. The source which generates the charged particle beam preferably operates in a high vacuum environment, and attaining this high vacuum in the vacuum chamber is difficult and time consuming, reducing overall throughput of the lithography system. Furthermore, contaminants such as water vapour and hydrocarbons outgassed from the resist-covered wafer and components of the system in the vacuum chamber are also a problem.